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Unformatted text preview: ting a character set of 96 characters will have altogether 12,672 (132x96)
characters embossed on its surface.
In addition to the drum, the printer has a set of hammers mounted in front of the drum in
such a manner that an inked ribbon and paper can be placed between the hammers and
the drum. The total number of hammers is equal to the total number of bands on the
drum, that is, one hammer is located opposite to each band of the drum.
The drum rotates at a high speed and a character at a print position is printed by
activating the appropriate hammer when the character embossed on the band at the print
position passes below it. Thus the drum would have to complete one till revolution to
print each line of output. This means that all characters on a line are not printed at exactly
the same time, but the time required to print an entire line is so fast that it appears as if
one line is printed at a time: A drum printer is shown in Figure 9.30. The drum of a drum printer is expensive and cannot be changed often. Hence drum
printers can only print a predefined set of characters in a pre-defined style that is
embossed on the drum. Due to this reason, drum printers do not have the ability to print
-any shape 0f characters, different sizes of print, and graphics such as charts and graphs.
Drum printers are impact printers because they print by hammering the paper and the
inked ribbon against the characters embossed on the drum. Hence they can be used to
produce multiple copies by using carbon paper or its equivalent. However due to impact
printing, drum printers are noisy in operation and often use a cover to reduce the noise
level.
Since drum printers use inked ribbon to produce printed output, they are usually
monochrome. Typical speeds of drum printers are in the range of 300 to 2000 lines per
minute.
Chain/band printers are line printers that print one line at a time. The print mechanism of
a chain/band printer h shown in Figure 9.31. It consists of a metallic chain/band on...
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